


Neptune's Heartbeat

by Methoxyethane



Category: Voltron: Legendary Defender
Genre: Alternate Universe - The Little Mermaid Fusion, M/M, Mermaids, Merman Lance, Tooth-Rotting Fluff, Witch Keith, Witchcraft, Witches
Language: English
Status: Completed
Published: 2018-10-15
Updated: 2018-10-15
Packaged: 2019-08-02 11:47:01
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,506
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16304615
Author URL: https://archiveofourown.org/users/Methoxyethane/pseuds/Methoxyethane
Summary: Deep in the ocean in the fossilized corpse of a sea god lived a Witch.





	Neptune's Heartbeat

_ “Double, double, toil and trouble,” _ a voice sang, echoing against the walls of Keith’s tiny little cavern. “ _ Fire boil and cauldron bubble~! _ ”

Keith sighed, the huff of annoyance indeed blowing a few stray bubbles out of his gills as he put away the kelp scroll he’d been looking at, knowing his guest wouldn't leave him any opportunity to try and read it. “Hey Lance,” he greeted as the other merman swam in, as always darting in fast enough to make waves that nearly knocked Keith’s wide-brimmed hat off his head. He caught it gently with one hand, flicking his own tail to give him enough of a spin in the water to face him. “Business, or pleasure?”

“Aw, you know me babe,” the marlin grinned, sharp teeth sparkling. “When it comes to you it’s  _ always _ a pleasure~”

Keith snorted, rolling his eyes to hide the tug of a smile on his lips. “You’re an idiot. If you’re only here to bother me, do it when I’m no in the middle of work.”

“You’re always working,” Lance scoffed, following Keith as he swam back to the shelf of scrolls he’d been reading from.

That was true. Being a sea witch was more than just an unusual job, it was also a difficult one. Keith had inherited it from his mother before him, but she hadn’t been around long enough to teach him everything she knew and he had to figure out a lot for himself. The old collection of scrolls had basic spell instructions but not much more, and any fine details he had to work out for himself on a case by case basis. 

Spells to be more attractive to the opposite sex weren’t the same as love spells, and spells to become more attractive to the SAME sex were another adjustment still. Someone who wants to be a better hunter needs a combination of factors, swiftness and vision and reflexes all enhanced just a bit, an incredibly complicated design for an incredibly common request.

The part where no one wanted to admit they sought his services and still let him be somewhat of a social pariah also made things harder, but at least Keith knew better than to be personally offended. He DID live in the hollow skeleton of an ancient sea god, after all, and as good for magical conduction as that was it was also kind of terrifying beyond all reason to swim into the open jaws of a jagged-toothed monster to get into his house. 

Not that most people were willing to pay the costs of his services, anyway.

“But fine, yes,” Lance continued, not allowing Keith’s attention to stray for him for too long. “I DID bring you some ingredients for your scary people-potions. Praise me like I deserve.”

Keith perked up, letting Lance steal his focus as he abandoned his recipes. Lance’s attitude may have been absurd and mostly made-up, but it was nonetheless well deserved. The ingredients he needed for his magicks were far from common, which was honestly for the best considering otherwise any brainless moron could accidentally throw together a potion while trying to make soup. Magic itself was in everything down to the smallest bit of plankton, but the ability to understand and  **use** it was beholden only to a select few. 

Keith may have had the magic, but if he couldn’t get his hands on the specific elements he needed to create spells he could do little more than parlor tricks. Luckily, that’s where Lance came in.

The Lance in question was still grinning boyishly, flickering his eyebrows and swishing his tail, the little string of pearls he had tied around the base above his fin floating up to tap noisily against his scales. “I got some mantaray marrow and ambergris -”

“Holy mackerel,  _ ambergris _ ?” Keith interrupted in amazement. 

“Yeah, there was a whale beached a bit near where I ended up for work,” Lance dismissed, like the process of GETTING the precious waxy rock from a dead whale was all fun and games. “But close your eyes and turn around so I can show you the  _ coolest _ thing I found!”

Blinking in confusion, Keith obeyed, trusting Lance at least wouldn’t do anything too nasty even if he was playing a prank. He waited, and soon felt the gentle slide of something looping loose around his neck, a light shiver running down his spine as it settled into a cool weight in his collarbone.

His eyes fluttered open, looking down to see a thin gold necklace hanging softly around his throat. On the end of the chain was a metal ornament like a coin, slightly domed on either side and engraved with elegant carvings and a tiny pink glass jewel facing outward in the very center. It was a human bauble, but nothing about the materials seemed like they had any use for the kind of magic Keith did so he was forced to wonder if it was for decoration only.

“Um. Thank you?” He complimented, something warm curling inside his chest at the thought of Lance giving him something useless and pretty just because. 

Lance smiled at him, giving his eyebrows a little waggle. “You haven’t even found the best part yet,” he said, one hand reaching out to delicately take the strange trinket in his long fingers. Keith watched as one blue claw wormed into the seam where the front and back the odd coin met, suddenly parting in two with both halves swinging open on a tiny hinge.

The strange necklace was hollow, and inside was a tiny, ribbon-tied lock of light brown threads.

“ _ Hair of the Sailor, _ ” Keith gasped, realizing what was inside. “How did you get this, humans never let their dead comrades stay in the water after they’ve drowned! They always steal all their bodies parts back from the ocean, this shit is impossible to find intact!”

“Plus you can keep the locket after you’ve used it,” Lance’s excitement about the gift was visible, and therefore contagious. “Maybe put something else inside for yourself, seal it with magic and carry around a secret~”

Keith blushed, closing the locket with a click and holding it in his own fingers until the metal warmed up in his grip. “You’re never gonna let up on covering me with shiny decorations, are you?”

“Not as long as they keep making you look pretty,” Lance laughed back, reaching over to toy with the beads tied into Keith’s hair just behind his ear fin.

“ _ Ffffffff _ ,” Keith blustered out, turning his face and paddling his fin once to float back away from Lance’s reach. “You’re so full of carp. Stop embarrassing me just to avoid admitting you were in human territory and probably almost died again.”

“Oh come on, you’re overreacting!” Lance was the one to avoid eye contact now, waving Keith’s concerns away with one hand. “Yeah, I was on the surface last night, but it’s not like every single square inch of every single beach on Earth is covered with human beings!”

“You were close enough to get jewelry off of someone.”

“Only kinda, someone left it behind so I grabbed it while I was already right there for work! I found it fair and square, no stealsies!”

Like whether or not it was  _ stolen _ was what Keith was worried about. 

Lance had a job paid by Queen Allura’s taxes, a rescue marlin with the task of finding lost merpeople and bringing them safely home - or as need often be, to where there was urgent medical care available. Considering people only generally got lost or trapped in either deep waters or up on the shore it was pretty much the most dangerous job in the entire ocean - even moreso than Shark Lawyers. 

If he was on the shore to find a beached whale that meant he and his partner must have been scanning beaches to find someone, trying to grab them and bring them home before the humans found them. Which meant as far as statistics were concerned when it came to one mermaid hiding in one spot it was about ten times as likely for someone to see the rescue team instead.

Keith sighed and turned back to his scroll shelves, knowing it wasn’t fair to be annoyed at Lance for doing what he had to do. Lance was a hero who spent his nights saving lives, and while Keith may consider what he himself did as helping people simply granting wishes just wasn’t on that same level of valor. 

And besides, Lance was the fastest swimmer he’d ever met, he’d stay safe...

Keith plucked out the right kelp scroll, knowing of one certain spell he’d always wanted to try but never had the full array of ingredients for until now. “Alright, you can keep up with the weird gifts as long as you don’t put yourself in any extra risk to get them.”

He swam up towards the ceiling to gather the materials he needed, selecting bubbles sealing off bits and scraps like Kraken’s beaks and seagull’s blood where they were floating out of his way. “And I’m paying you back for anything I use for a client, so it’s not all presents, either. Just business.” 

“If it helps,” Lance defended squeakily as he followed Keith and his armful of elements deeper into the bowels of his home, where the bioluminescent plants stopped lighting the walls and floor and darkness took over the space in a wave. “I was paired with Shiro, so it’s not like anything was gonna go  _ wrong _ .”

Keith paused, half a second away from lighting his cauldron up. That did help, actually. Shiro was the first merman he’d ever trusted outside of the Deep Waters. The orca was as reliable as he was kind, strong enough to capsize a fishing boat and large enough to help carry the weight of an injured mermaid easily, and combined with Lance’s speed it was hard to believe any human hunting equipment would be able to pose a real threat.

“Maybe a little,” he conceded, directing the bubbles he’d gathered to all float around the rim of his cauldron to wait for him while he used his magic to spark a glowing green heat spinning underneath the metal pot. 

Lance grinned, darting a few pleased circles around Keith while he settled in to watch over his shoulder as Keith double-checked the spell on the scroll.

“You know it might be easier to read that if you actually had any lights set up in here,” Lance observed idly, eyes scanning the depths of Keith’s fossilized home. “I know you’re not dramatic enough to have it just be for ambiance.”

“The magic in bioluminescent plants is too strong,” Keith answered. “Interferes with whatever I’m working on.” Also, he didn’t really need then anyway. He was born in the Depths after all, his eyes could more than easily handle the dark.

“Oh THAT interferes,” Keith could hear the teasing smile in Lance’s voice without looking over. “But your own majestic glow here doesn’t make a difference?”

Keith rolled his eyes, relaxing now that Lance had only even brought the subject up as a route to tease him. _“T_ _ hat _ ,” Keith said sternly, twirling is fingers to send the array of bubbled ingredients spinning into the controlled boil of the cauldron’s bowl. “Doesn’t count for anything because it’s just another part of  _ my _ magic.”

The ‘that’ in question of course, being the purple-blue glow emitting from deep inside Keith’s belly, shining through his black scales in the dark to make his whole body shine. Lantern sharks and lantern mers like him weren’t even inherently that magic, but when you combined their natural luminescence with constant sorcery what was supposed to be a faint glow tended to light up like an anglerfish’s lure.

“Now stop trying to distract me, I wanna see what a ‘Neptune Heartbeat’ really looks like.”

Lance stayed quiet, settling in to watch the ingredients as they sizzled off in the pot to coalesce into their spell. The green glow of the pot turned white with heat first, brilliant and eye-watering until it calmed into a vibrant blue, shining cerulean as the sky against the ocean surface. 

And that was only what Lance could see. Inside the cauldron Keith could feel the raw potential of the magic, strong and swirling like rapids only barely under his control. He drew the last element needed out of his new locket, three strands of sailor’s hair swishing out of their metal confines to fly straight into the pot’s center, disintegrated into raw magic before it even spun in to join the whirlpool.

The power of the spell exploded, that blue light strong enough to light up not just the room but probably the entire cubic mile around the dead monster he lived in, too. This spell… Keith could feel it now, could sense all the threads of magic weaving together within the swirl of the cauldron barely trapping it in his grasp. This wasn’t just some ancient magic trick penned down by a hack, this was power Keith had never felt all in one place before. This wasn’t just strength, this was the force of the e _ ntire ocean itself _ .

The magic rippled, now swirling so fast in the cauldron to peel off the walls. The faster it spun the smaller it condensed, a full cauldron of raw magic whipping down into a disc, and then smoothing into a sphere of pure blue light. A beacon, Keith realized as the spell continued to spil almost out of his control. He was going to need an object to seal the spell into, something with… no, it couldn’t be a taitional magic object, instead it had to be Natural Magik, something filled not with energy but just  _ emotion _ . Something hated, something feared, or something of sentiment…

Sentiment. Keith reached up to the band of his pointed hat, where an array of small objects were tied to the base. The tips of his fingers sought and found the gentle ripples of a shell, and he plucked it from the brim of his hat to hold out over the cauldron. The core of the spell still spun pearl-like in the center of the pot, until Keith called it to join with the empty shell and the blue bead of light whipped up to rocket into the bivalve, vibrating in the small hollow space between the two open halves before Keith snapped it closed with a dramatic flare-up of light.

Holy shit it worked… Looks like the first stupid present Lance had given Keith had enough… of whatever feelings were attached to it. Anyway, flying hellfish that had been the most advanced spell Keith had ever even ATTEMPTED, he couldn’t believe he hadn’t just killed them both on this stupid whim!

“Whhhooooaaa!” Not that he’d tell Lance that he could have just blown the two of them up. Especially with that impressed look on his face, whistling at Keith like he was the most amazing person he’d ever laid eyes on, all sparkles and grins as praised, “God damn that was so cool, I’ll never get tired of watching your magic! Like WHOOSH BANG ZAP, and then it all fits down into a little bitty shell, like holy manatee!”

Keith hid his blush by tilting his head down, feeling the warmth of fresh magic as his hand curled around the small shell. “I-it’s not like it’s anything no one else can do either, just a skill I picked up like anything else is.”

“A skill so valuable people pay you their most treasured possessions just to get a wish granted,” Lance insisted, gesturing to the tail end of his cave where the various ‘payments’ of Natural Magik-filled knick-knackery Keith didn’t know how to use but were too valuable to throw away. Emotional attachments to objects were incredibly powerful, even if it wasn’t a power that could be manipulated or harnessed like the magical energy everything on the planet produced was that didn’t mean it couldn’t be… taken advantage of. “You’re a total badass dude, just admit it.”

“At least as badass as the rescueman who spends all night guiding civilians home out of danger,” was as far as Keith would concede to. Just because anyone could do it in  _ theory _ didn’t mean everyone was right for the job.

“So, uh,” Lance poked his head into Keith’s space, trying to examine the clamshell still in his hand. “What does it like. DO, anyway? What happens if you open that thing now?”

Keith looked down at the shell in his hand, uncurling his fingers to lay it flat on is palm. “ _ Neptune’s Heartbeat _ ,” he recited from memory. “ _ The call of Tides, to hold the Heart of the Sea in thine hand for the length of a single beat. _ ”

Lance blinked. “Which uh… means what, exactly?”

“Yeah,” Keith nodded with a easy shrug. “That’s what I wanted to find out when I started. It wasn’t hard to figure out once the spell was actually going, though, and it basically does what the description says.”

“You… can tear someone's heart out?”

Keith snorted a laugh, reaching up to tug on Lance’s shark tooth necklace with one finger. “Nope,” he said with a smile in his voice as he tied the shell into the necklace cord, sitting it between two human-hewn beads of sparkling red and letting it drop to settle on Lance’s chest. “It’s like a storm-in-a-bottle, but way more powerful. Open it up and you’ll call a huge tidal wave, do it too close to shore and it could wipe out a whole human village.”

Lance looked startled and lightly terrified. “A fucking tsunami-in-a-can and you’re giving it to ME?” He looked down at the shell he was now wearing, and in a concerned voice asked, “What… what happens if I break it?”

“You won’t,” Keith chuckled. “It CAN’T break now, until it’s opened intentionally. Only one use and the magic is gone, but… if you ever have an emergency and need to escape, now you have a... Backup plan, I guess.”

Lance shook his head. “Keith, I can’t take this! You can’t just randomly hand out super powerful spells to idiots, don’t you like… need this shit?”

“Not really?” He hunted all his own food and didn’t need to pay rent on his land considering he lived in a fossil in the Depths, so it’s not like he needed to sell every single spell he weaved. “Please, just… I’d feel a lot better if I knew you had it.”

They held gazes for a long moment, and Keith let himself show Lance a little of the vulnerability he was so good at hiding. Keith never wanted to admit even to himself how much he worried about Lance and not being able to do anything for him, but… if he had this, it’d be like a little piece of Keith was with Lance to protect him no matter how far away he was.

“I’m never not gonna be paranoid about breaking it,” Lance muttered, a blush bluing his own features as he averted his eyes. “I’m gonna accidentally wipe out Atlantis and it’ll be your fault.”

“Not if I blow it up myself before you get the chance,” Keith grinned. “If anyone’s gonna use my magic for accidental genocide it’s  _ me _ .”

Lance laughed too, even though it was a bad joke and neither of them should be laughing at all. “Thank you,” Keith finally said, floating up to eye level and tilting his head back. “For keeping it; and for the locket.”

He didn’t give Lance a chance to say something clever, already darting forward to press a small kiss on his lips. When he pulled away Lance was still dumbfounded, flushing bright purple as a dopey grin bloomed across his face.

“YAHOO~!” Lance rocketed into a delighted spiral in the water the second he recovered his wits, spinning happy peals like a baby guppy. He looped back to Keith to grab his hands and drag him with on one final dizzying spin, both of them giggling when they let their hands go to float apart again. 

“Looks like I’m gonna be busy,” Lance sang, as the two of them swam out of his work room and back into the well-lit mouth of his home’s living space. 

“Busy?”

“Yeah,” Lance stopped the the mouth of Keith’s cavern, hovering in the open jaws between giant skeletal teeth. “If I get a kiss for bringing you presents now, I’ve got a loooootttt of treasure hunting to do!”

He laughed as Keith tossed a half-empty tube of tooth cleaner at his head, dodging easily and swimming out the doorway. “I’ll be back soon, my darling!”

“Don’t bother!” Keith shouted back, floating to settle down in a seat of coral with the smile still on his face. 

A warmth had settled in his chest Keith didn’t notice until Lance was already gone. It felt just a little bit like magic.

—


End file.
